gms | German Medical Science

Objective: Motor areas of the rhomboid fossa cannot be visualized preoperatively and consequently not be identified by neuronavigation intraoperatively. Therefore, a three-dimensional model of the brainstem was created, which contains important cranial nerve nuclei and can be registered with a patient's MRI-dataset to be used for intraoperative navigation. We now present our first clinical experience with the newly developed tool.

Method: After fixation three human brainstems were cut into serial slices of 50 µm thickness. Staining was done with cresylviolet. All slices were digitized with a high-resolution scanner. Cranial nerve nuclei were segmented slice-by-slice. Cranial nerve nuclei and the volume of the brainstem were three-dimensionally reconstructed and visualized using a direct volume rendering technique (“texture mapping”). Brainstem volume with cranial nerve nuclei was non-rigidly fused to MRI-datasets used for intraoperative navigation.

Results: Dorsal motor nucleus of the vagus, nuclei of cranial nerves VI, VII and XII and motor nucleus of the trigeminal could be clearly identified and reconstructed three-dimensionally. Coregistration with MRI-datasets was achieved and provided an individual 3D-model of the brainstem containing the segmented cranial nerve nuclei. Two patients with cavernomas of the pons suffering from haemorrhage and one patient with a pontine pilocytic astrocytoma were operated using the newly developed tool. In two cases high accuracy was demonstrated by electrophysiological stimulation. In one case coregistration to the patient's MRI-dataset was difficult due to brainstem distortion by a large cavernoma with extensive haemorrhage. In this case we found a relevant localization error mainly for the z-axis.

Conclusions: A new tool for surgery around the floor of the IV. ventricle is available. It three-dimensionally visualizes important cranial nerve nuclei within a model as well as individualized in a patient's MRI-dataset. Especially in combination with frameless stereotaxy it provides substantial spatial information in addition to intraoperative, electrophysiological findings.